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Generator Design

  1. Mar 17, 2013 #1
    i'm looking to design a generator, can someone just help me out, the following are the main criterias:
    It'll have a power rating 30KW
    RPM like between 120-200, so basically its a low RPM design;
    i plan on using Carbon fibre for all the components on the rotor other than the power generating components..............should basically give very low inertia for the same structural strength as steel................
    also can someone tell me how to determine the power rating of the generator based on the magnets and copper windings?
  2. jcsd
  3. Mar 17, 2013 #2
    Sahil I don't want to sound rude but do you have built something on the scale of this before?
    Also you should realize that the power level 30KW is something one just doesn't build in his home.Devices like these are built in factories by people who have experience and designed by people who have even more of that.

    Can I ask you why and for what are you building this?

    Also carbon fiber is a dielectric , which means it doesn't conduct electricity and doesn't have magnetic properties , do you know how generators work? The rotor has to be made out of materials that have electromagnetic properties like copper wires and stainless steel armature and so on.You cant make a rotor with carbon because the metal armature in the rotor is what helps to make the induced magnetic field stronger , carbon will not do this and the generator will be with poor efficiency.If any at all.
    The wires are moving around in a magnetic field which induces current in them .The basic principle of a generator/electromotor.

    If you haven't built anything like this before I suggest to start with a low power 1-2kw generator to understand the working principle and see how it all goes together.You can make a generator out of an old electric motor.
  4. Mar 17, 2013 #3
    Hey.... Yeah I get what your trying to tell me but can I use carbon fibre In places like the structure to support the magnets?
    Last edited by a moderator: Mar 19, 2013
  5. Mar 17, 2013 #4
    And also can you help me design a 2 kw generator?
    Last edited by a moderator: Mar 19, 2013
  6. Mar 17, 2013 #5
    Well yeah actually I'm not going to build this at home, like ill get it built buy a manufacturer but I just want to know whether it is possible to reduce the weight and inertia of the rotor by substituting components of the rotor that do not contribute in producing the magnetic field from steel to carbon fibre (eg. Rotor shaft, the frame that holds the magnet in place, etc.) also for my requirements, the copper windings would be on the stator where as the rotor will have the magnets........
    Last edited by a moderator: Mar 19, 2013
  7. Mar 18, 2013 #6
    You probably CAN reduce the inertia, but I'll guess from my limited knowledge that the electrically conductive/ magnetic portion is by far the heaviest part of the generator. And carbon fiber is expensive. You'll probably increase the cost of a normal generator by a large amount for an insignificant loss of mass and/or inertia.
    Last edited by a moderator: Mar 19, 2013
  8. Mar 18, 2013 #7
    What percentage of the rotor inertia does the magnet contribute ( on a rough estimate)
  9. Mar 18, 2013 #8


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    Also, why are you trying to reduce the inertia? Most generators operate at a constant RPM, so low inertia wouldn't really give any benefit. Once at speed, assuming you use decent bearings, almost 100% of the resistance to turning the generator would come from the magnetic field itself, so all you would achieve with a low-mass design would be to make it substantially more expensive for almost no benefit. Also, a custom manufactured generator would be very expensive - you would probably be better off just buying a commercial generator of the size you need.
  10. Mar 18, 2013 #9
    Yeah....... Ohhh but is there anyway where I can reduce the input power required to get the rotor moving for the same level of output? Like someway of increasing mechanical advantage or something ?
  11. Mar 18, 2013 #10


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    You're basically looking to increase the efficiency, and large generators (admittedly much larger than you're looking at here) can already hit 98%, so there isn't a whole lot to be gained here. What's your application?
  12. Mar 18, 2013 #11
    Just wanna use an electric motor of lower power rating to get thing moving and harness the surplus power generated.......
  13. Mar 18, 2013 #12
    there is pretty much nothing to take away from the rotor as it has to be 95% metal or metal alloy and copper.Also the 98/99% of the power needed to turn the rotor is opposed or consumed by the magnetic field which actually induced the current in the windings.Only I think like 1% would be due to friction in bearings (assuming they are lubricated and new)

    Sahil I think you need to read up about classical physics , electromagnetism , generator / electric motor working principles.
    Now I hope you do understand english pretty ok I have some old but very informative videos about this topic.Remember in the generator motor part there are no fundamentally new things so things discovered 50/60 years ago still apply just as back then as now.

    Now watch these and you will be better off if you will pay attention to what is said there.
    Last edited by a moderator: Sep 25, 2014
  14. Mar 18, 2013 #13
    Hey ill have a look at then and will revert back if I come up with any queries.... Btw I'm not pursuing science.... I'm a commerce student planning to pursue MBA this year
    Last edited by a moderator: Mar 19, 2013
  15. Mar 18, 2013 #14
    """"Just wanna use an electric motor of lower power rating to get thing moving and harness the surplus power generated....... """""

    Now I see what your talking about.Probably you have watched some "free energy videos" on youtube or something like that.

    Sahil even though many of those people who either because their very uneducated or just fanatically crazy say that mainstream physics is lying about the fact that there is no free energy , I must admit there really is NO FREE ENERGY.
    When I was very little I though that one can get free energy but the truth is I grew up and learned that well , you can't.

    the motor that will drive the generator will use power , the more load you will put on the generator the more power will be taken to drive it.magnetic field doesn't go for free it tries to stop the generator rotor from moving.It's like arm wrestling you can't win a opponent with a weaker arm, the power doesn't come from "thin air" you have to supply the power to overcome the resistance.
  16. Mar 19, 2013 #15


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    Using carbon fibre in rotor ? Well.. I hope you have any clue what are drawbacks of this idea.
    Rotor is quite complex in design, it's not flat like many carbon fibre elements. It has directional mechanical proporties, which can be quite dangerous because many forces are acting in rotor while it is working in the machine. In addition, I'm not so sure about this reducing inertia idea - benefits from it are not worth pursuing it in my opinion.

    Second thing, You said you're not familiar with engineering.. please, gain some knowledge in this matter. It's not that easy like "I have an idea, let's do it". You will be wasting your time without deeper understanding of matter discussed here.
  17. Mar 19, 2013 #16
    Why will the magnetic field try to stop the rotor from moving ?
  18. Mar 19, 2013 #17
    As in is there some particular reason ? Or something ?
  19. Mar 19, 2013 #18
    As you know, magnetic fields attract or repel each other depending on their poles.

    Also, when you have electricity flowing through a wire, it generates a magnetic field. Conversely, in order to generate electricity, you move a magnetic field across a wire.

    Well, it just so happens that when you try to generate electricity by moving a magnetic field across a wire, the very electricity that gets generated creates its own magnetic field, which opposes the one you are moving in order to create it.

    It's the mechanism that keeps you from making energy out of nothing. You'll find that in this universe, there is always some such mechanism.

    You can feel this by simply spinning a generator with no load, and then attaching a load to it (such as a light bulb). You'll find that the generator gets much harder to turn. I wish everybody tried this so that they would stop trying to to create energy by some "clever" arrangement of magnets.
  20. Mar 19, 2013 #19
    What is this counter electromotive force?
  21. Mar 19, 2013 #20


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  22. Mar 19, 2013 #21
    Hey I read the article but can someone just explain me how will this CEMF have an effect on the generator rotor when it's spinning
  23. Mar 19, 2013 #22


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    Zero effect on rotor. CEMF will be induced in stator winding.

    Let's be straight: what are you thinking about ?
  24. Mar 19, 2013 #23
    So basically it won't have any effect on the rotor while its in motion?

    Yeah I've already mentioned about my intentions a few post earlier just have a look at it and youll know what I'm talking about
    Last edited by a moderator: Mar 19, 2013
  25. Mar 19, 2013 #24


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    Ok, so as I said it in one of my posts. Unless there is a real reason (like generator is drived by a very specific drive) there is no need to reduce rotor mass-> it's inertia.
    Inertia moment of rotor is not all bad, it is required to provide adequate dynamic properties to the machine.
    Plus: designing (and building) a rotor made of not-steel or so needs deep knowledge and can be extremly dangerous.
    Third thing: I'm sorry, but this is not about briliant ideas.. it needs some knowledge.

    EDIT: few mor words..

    increasing generator efficinecy - this is your goal, right ? Well, this is very hard task even for people doing this for years. I won't elaborate on it. Please search for proper articles/books if you want. Then we can talk about important details in machines design.
    Last edited: Mar 19, 2013
  26. Mar 19, 2013 #25

    jim hardy

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